1. Field of the Invention
The present invention generally relates to voltage generating devices, and particularly relates to voltage generating devices that are used in image forming apparatuses.
2. Description of the Related Art
Development devices that develop electrostatic latent images using a two-component developer are present as development devices equipped in electrophotographic system and electrostatic recording system image forming apparatuses. The main components of two-component developer are a nonmagnetic toner and a magnetic carrier. A power supply apparatus enables the toner to more easily develop the latent image by applying a developing voltage, in which a direct current and an alternating current are superimposed, to a development sleeve. However, when a high voltage is applied to the gap (development gap) between the photosensitive member and the development sleeve, a ring shaped or spot shaped pattern (hereinafter referred to as a ring mark) is sometimes produced on the recording paper.
According to US Publication No. 2011/0020028, by configuring a positive amplitude absolute value |Vp+| relatively smaller than a negative amplitude absolute value |Vp−| of a positive amplitude Vp+ and a negative amplitude Vp−, which are the amplitude of the alternating current voltage contained in the developing voltage, ring marks produced in background areas are easily suppressed.
In this regard, the power supply apparatus that generates the developing voltage may be provided with two switching regulators for driving a transformer. The switching element provided in each of the switching regulators executes a switching operation at a predetermined drive frequency. Accordingly, sometimes a periodic ripple that is dependent on this drive frequency is contained in the voltage outputted by each of the switching regulators. By being supplied with voltages from the two switching regulators, the transformer generates the developing voltage. Accordingly, if a ripple is contained in the voltages outputted by the two switching regulators, an influence of the ripple will appear also in the developing voltage. Although the drive frequencies of the two switching regulators are designed to be the same frequency, in reality the two drive frequencies are not identical due to variation in circuit components. When the difference between these two drive frequencies becomes a beat component and appears in the developing voltage, so-called a banding is formed undesirably on the recording paper.